The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the removal and/or treatment of vertebral discs and/or portions of the vertebral disc such as the nucleus pulposus, the annulus fibrosis, or the vertebral endplates.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. Spinal discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient's spine. Spinal discs comprise a central hydrostatic cushion, the nucleus pulposus, surrounded by a multi-layered ligament, the annulus fibrosis. As discs degenerate, they lose their water content and height, bring vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may pinch nerves. This disc degeneration can eventually cause back and leg pain. Weakness in the annulus from degenerative discs or disc injury can allow fragments of nucleus pulposis from within the disc space to migrate into the spinal canal. There, displaced nucleus or protrusion of annulus fibrosis, e.g., herniation, may impinge on spinal nerves. The mere proximity of the nucleus pulposis or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in numbness and weakness of leg muscles.
Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. Minimal invasiveness can be characterized by limiting damage to healthy tissue while removing selected tissue, or can be decribed by minizing trauma during access to the targeted tissue. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuring scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. These monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Often, inflammation attributable to vertebral discs can be treated successfully by either non-surgical means, such as rest, therapeutic exercise, oral antiinflammatory medications or epidural injection of corticosteroids or by surgical means which treat the vertebral disc (whether open or minimally invasive.)
In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. Or, the annulus of the disc may be intact but a lack of vertebral disc height may cause complications. In severe cases, one or more vertebral discs must be excised and any adjacent vertebral bodies are then mechanically stabilized, via surgery, following excision of the disc to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted from other portions of the body, such as the hip, and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and alleviating the pain. Alternatively, a disc prosthesis may replace the vertebral disc. In some cases, a portion of the vertebral disc, such as the annulus fibrosis, may be removed and replaced with an implant/prosthesis.
In cases where an implant/prosthesis is used, it may be desirable to remove the pre-existing vertebral tissue. For example, migration of the implant subsequent to its implantation is undesirable. Removal of any undesired vertebral tissue, so that there is adequate contact between the bone of the vertebral body and the implant, may minimize migration of the implant.
Currently, mechanical means, as discussed above, is commonly employed to remove degenerated vertebral disc tissue. For example, removal of the majority of the disc, or the disc portion being removed (e.g., the nucleus), occurs via graspers or rongeurs. After a substantial portion of the tissue is excised the remaining tissue (e.g., the tissue adjacent to the vertebral endplates) may be scraped. Yet, such procedures may take an undesirably long period of time to remove an optimum amount of tissue. Furthermore, as individuals age the disc loses its water content and become relatively stiffer. Use of mechanical means to remove a degenerated disc may result in a significant amount of remaining fibers or wisp-like tissue. Such tissue by-product may be difficult or impossible to remove via mechanical means.
Yet another drawback with mechanical removal of degenerated disc tissue is that the cortical endplates on the vertebral bodies is easy to damage. In some cases, it may be desirable, or necessary to retain the cortical endplates. Use of mechanical means to remove tissue attached to the cortical endplates may cause unintended damage to that endplate.
As discussed above, conventional means to remove vertebral tissue (e.g., mechanical, chemical, laser, conventional electrosurgical) pose significant drawbacks to efficient removal of disc tissue in preparation for implant and/or prosthetic replacement of all or a portion of the vertebral disc.